Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with agraphical user interface showing one embodiment of our new design; and,

FIG. 2 is a front view of a display screen or portion thereof with agraphical user interface showing another embodiment of our new design.

The dot dashed broken line showing the display screen or portion thereofforms no part of the claimed design. The dashed broken line showingportions of the graphical user interface forms no part of the claimeddesign.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, as shown and described.